This invention pertains to a material for the treatment of gaseous media containing volatile organic compounds, such as ethylene, as well as a process for the treatment of gaseous media using this material.
The invention also concerns a process and a device for obtaining the material.
This material and the associated treatment process are used for the treatment of atmospheres in which living materials are stored, particularly in refrigerators or coolers.
Ripening of living materials generates volatile organic compounds, such as ethylene, some of which cause autocatalysis of the ripening process. These compounds are also responsible for unpleasant odors, and usually generate microorganisms and contaminants such as bacteria, molds, and yeasts. Therefore, they are harmful to the proper storage of living materials because they can cause biological degradation, which is detrimental to storage and to consumer health.
These compounds are very light, and therefore they can circulate readily through ventilation or air conditioning systems.
In known storage systems, the atmospheres receive no particular treatment, and this results in a number of sanitary risks.
The purpose of the invention is to remedy these disadvantages by offering a material for the treatment of gaseous media containing volatile organic compounds and a treatment process using this material which allows for chemical transformation of the volatile organic compounds into harmless gases; the structure of this material makes this treatment process particularly effective.
Thus, the invention concerns a material for the treatment of gaseous media comprising volatile organic compounds, this porous material presenting an adsorption capacity of about 20 to 30% of its dry weight and comprising about 47 to 52 wt % of a composite structure of silicon and carbon, about 12 to 20 wt % carbon, about 5 to 7 wt % hydroxyl, and about 1 to 2 wt % oxygen.
It is preferable for this material to comprise a peripheral volume corresponding to essentially one-third of the total volume of the material, of about 75 to 85% porosities, with pores having dimensions between 10 and 50 xc3x85 and, in the remaining central volume, about 80 to 90% cavities whose dimensions are between about 200 xc3x85 and 2 xcexcm.
It is preferable for the specific surface of the material according to the invention to be between 1200 and 2200 m2/g.
The material may advantageously include about 20 wt % aluminum oxides and about 5 wt % iodides.
It is also advantageous for the relative humidity of this material to be less than 2 wt % with respect to the dry weight of the material.
The invention also concerns a process for the treatment of a gaseous medium containing volatile organic compounds, consisting of directing a flow of said gaseous medium over a porous material according to the invention, to bring about adsorption of this flow which penetrates the pores and the cavities of the material, in the process of which a chemical reaction occurs between the volatile organic compounds of the flow and the material itself, to transform the volatile organic compounds into nontoxic gases, particularly CO2 and/or SO2.
The process according to the invention is more effective when the porous material according to the invention presents a very high number of pores and cavities which allow diffusion of the gaseous flow throughout the material with a large specific surface. The chemical transformation of the gas flow is favored by the relatively long contact time between the gas flow and the material when the latter is penetrated by the flow.
Thus, the treatment process according to the invention provides a contact time between the gas flow and the material which is between 0.08 and 0.12 sec.
The invention also pertains to a device and a process for obtaining the material for the treatment of gaseous media according to the invention.
This process consists of:
preparing a clay base constituent comprising about 30 wt % clay with a particle size which is greater than 180 xcexcm, and about 70 wt % clay with a particle size which is between 10 and 20 xcexcm;
impregnating this base constituent with an aqueous solution containing about 10% by volume of acetic acid, between 5 and 10% by volume of citric acid, and between 15 and 20% by volume of hydrogen peroxide, the volume of the solution being essentially equal to the volume of the base constituent,
applying a pretreatment of the base constituent impregnated with the solution by mixing it at a first pre-determined speed to create a porous structure,
mixing, at a pressure between 2 and 10 bar, the constituent which has been pretreated with an acidified liquid having a strong oxidizing potential, at a second speed lower than the first, to cause the liquid to penetrate the pretreated constituent and to form a gel, the quantity of pretreated constituent being between 42 and 48% of the total volume mixed, while the quantity of liquid is between 58 and 52% of the total volume mixed,
mixing the gel with complementary products comprising a solution with a strong oxido-reductive potential representing about 10% of the total volume, a mixture of carbon and alumina representing about 12 to 15% of the total volume and calcium sulfate representing about 2% of the total volume
drying the resulting mixture by ultrasound treatment of the material which has been mixed and transferred linearly, and
pressing the dried material under a pressure of 8 to 10 bar.
It is preferable for the process according to the invention to be implemented continuously.
It is preferable if the process also consists of heating the base constituent impregnated with aqueous solution, at the time of pretreatment, to a temperature between 200 and 250xc2x0 C.
The process of the invention also consists, advantageously, of emitting ultrasound waves at the time of this pretreatment, at a unit power of 2000 W and with an amplitude of 15 to 30 xcexcm.
Heating and treatment by ultrasound waves contribute to the creation of a porous structure.
It is preferable, at the time of pretreatment, for the process to carry out another mixing operation at a third speed lower than the first and second speeds, to enlarge the cavities and porosities of the resulting structure.
The process according to the invention consists advantageously of filtering the liquid which results from the pretreatment of the preimpregnated base constituent.
The liquid associated with the pretreated constituent preferably comprises about 10% by volume of a solution with a strong oxidizing potential.
The pretreated constituent and the liquid are advantageously mixed by being heated to a temperature between 90 and 120xc2x0 C.
The mixing of the gel and the complementary products is advantageously carried out at a temperature between 70xc2x0 C. and 80xc2x0 C.
The treatment with ultrasound to dry the mixture may advantageously be carried out over a length of 20 to 30 cm, under a specific output of 3 to 5000 W, an amplitude of 15 to 60 xcexcm and a frequency of about 20 MHz.
The material is preferably dried under a partial vacuum of 120 to 150 mbar and at a temperature between 90 and 100xc2x0 C.
Finally, the process according to the invention advantageously comprises a final stage of extrusion of the material.
The invention also pertains to a device for implementation of the production process according to the invention, which includes:
an impregnator comprising a first mixer turning at a speed between 1200 and 1400 rpm to form a first mixture,
a first reactor comprising a second mixer turning at a speed between 800 and 1000 rpm to accomplish mixing under a pressure between 2 and 10 bar, to obtain a second mixture of the gel type;
a second reactor comprising a mixer for a third mixture;
a device which accomplishes linear transfer of the third mixture and at least one ultrasound device delivering a power of 3 to 5000 W, on at least one part of the trajectory of the third mixture, and
a high-pressure extrusion device.
It is preferable for the impregnator of the device according to the invention to include a heating device which heats to a temperature between 200 and 250xc2x0 C., as well as a device for the emission of ultrasound waves.
It is advantageous for the impregnator to be combined with a device for filtration of the liquid evacuated from the impregnator.
It is preferable for the impregnator to comprise another mixer turning at a speed between 500 and 800 rpm.
The first reactor advantageously includes a heating device for heating to a temperature between 90 and 120xc2x0 C.
The second reactor advantageously includes a heating device for heating to a temperature between 70 and 80xc2x0 C.
Finally, the device for linear transfer of the second reactor is advantageously made up of a double screw whose rotation speed is between 5 and 150 rpm.
Finally, the extrusion device preferable includes a variable screw which subjects the material from the first reactor to a pressure between 8 and 10 bar.